After the disappointing rolling road dyno session I decided to look a bit deeper into the engine state. The first step was a compresion test of all 6 cylinders. Removal of the spark plugs was straightforward and the compression showed as a bit lower than expected. about 130 on a few cylinders.
This led me to believe there was either a problem with the head or the pistons/bores. The next step is to prepare the cylinder head for removal. While at this point I decsided to check and replace the cam timing chain, tensioner and gears. This will be replaced with a duplex chain and vernier cam wheel for accurate timing.
Also the cam followers. Due to wear on the rocker tips and a bit much play on the rockers and the rocker shaft; I have also decided to replace the shaft and rockers with a new shaft. This will also have new bronze bushed rockers fitted with spacers replacing the springs between rockers.
Brief procedure for Triumph top end removal.
1: Release throttle and choke cables.
2: Disconnect Remove Air filter, carbs,
3: Disconnect radiator hoses and inlet manifold hoses
3: Remove inlet and exhaust manifolds
4: Remove radiator/ fan and water pump.
5: Remove rocker cover by releasing 2 securing bolts on the top
6: Remove the rocker arm assembly by removing the 6 bolts securing the 6 pillars. Then lift off the shaft assy.
inspect the rocker tips for wear and the push rod tips and adjusters.
7: Remove cylinder head securing nuts and lift of the cylinder head.
8: Inspect the bores and head mating surfaces for wear and distortion.
New parts used
Stainless steel valves x 12
valve guides x12
payen head gasket and others associated with job
Cam followers x 12
Vernier Duplex timing kit
Rocker shaft and bronze bushed rockers x 12
Solid rocker spacers
Oil filter and Oil
Cylinders 2, 3 and 4 were also passing gasses between each other, as could be seen by the blackened block face; under the gasket and gasket damage at the cylinder wall points
At this point I pressed in new valve guides and sent the head for a surface skim and valve seat re-cut.
While the head was away for the engineering work I cleaned up the head casting with brake cleaner and a scotch-brite scourer. as pictured above.
At the weekend I fitted my new 123 tune distributor. I fitted a new fusebox and relays to improve the power feed to try and eliminate any losses in the ols switchgear and corroded connections.
The fitting was very straight forward as described in the manual. The only fiddly bit was a modification I had to make to the old Delco securing clamp. This was expected as the 123 is designed to be a direct replacement for the Lucas, not really for the delco.
The modification only involved opening the clamp hole up by about 10mm in diameter. (where the clamp clamps around the dizzy.)
The keener eyed folk will notice the timing is set to 0Deg BTDC until 500rpm. This is a very big advantage with starting. in the past unacheivable with classic mechanical dizzys
the button below will take you to the .xml code for you to use and modify as you need. I hope it helps.
The only part of the GT6 that I left relatively untouched was the engine ,gearbox and overdrive. The reason for this was I had the car Started and moving around a small yard before all the rebuild work took place. Alas after only a few miles of driving, the clutch thrust bearing started to make noises that resembled a small cage of birds.
since the car has been put away for the up-coming winter months I thought it would be a good time to undertake the necessary work.
There are a few ways this can be done. The first is to remove the engine and Gearbox as one unit. Then remove the GT6 gearbox from the 2 litre Straight six engine. Change the clutch and rebuilt in reverse sequence. I decided to go the other route and remove the gearbox from within the GT6 cabin, while leaving the engine in place.
Here is a list of Parts, tools and instructions on how to achieve this.
If worn, Bearing carrier and actuation arm. Check for wear at the point that the arm engages the carrier ring
Gearbox Oil, ( EP90 for topping up. EP75w-80 or EP75w-90 for filling from empty.)
List of tools
Ideally 2 people
Socket set to fit above sized
clutch alignment tool
Disconnect battery (Important)
Remove passenger side glove box.
Remove gearbox tunnel carpet.
Remove gearbox tunnel
Passenger seat removal is optional. be careful not to scrape or damage it if left in.
Disconnect propshaft. (4 x 9/16″ bolts, nuts) this may require rocking the GT6 forwards and backwards to gain access to all bolts from the cabin area.
Disconnect speedometer drive cable.
Disconnect reverse switch and overdrive unit wiring (If fitted) see picture below.
Remove the Clutch slave cylinder and actuation pin, that is located in the cabin on the bell housing by releasing the 2 1/2″ bolts
Jack up the front of the GT6, and rest securely on axle stands Chock the rear wheels to prevent the car from rolling. (Important)
remove the jack, and place under the rear of engine with a substantial block to support the engine weight.
Raise the jack to take the weight of engine and gearbox. (not lift, just support)
Remove the engine starter motor, 2 x 9/16″ bolts
Remove the gearbox / chassis mounts in the cabin, they are located on the underside of the box, and to the rear. 2 x 1/2″ bolts
Now begin removing bell housing bolts. Start from the bottom, as this will leave the top 3 studs still supporting the weight of the gearbox. 1/2″ nuts and bolts. Note: two people make this job a lot easier. 1 on the engine side with a 1/2″ spanner and 1 on the cabin side with 1/2″ ratchet driver. (See pic)
Once all but the top 3 nuts, on studs have been removed, remove the 2 nuts either side of the central stud/nut. clear the engine earth strap out of the way.
Now slowly undo the top nut on the stud. As it is undone you might find the gear box slowly start to pull away from the engine plate. Just support the rear of the gearbox.
Once the nut if fully off, I would recommend one person in each foot well. hold the rear of the gearbox, pull and wiggle slightly until the gearbox bell housing has pulled away from the engine block.
We found it easiest to lift the prop shaft end of the gearbox, and rotate it into the passenger side foot well. Some jiggling was required to clear the bell housing front under the lower dash rails.
Once the gearbox is clear you will be faced with 6 1/2″ bolts around the edge of the pressure plate. gradually undo these in a criss cross pattern to prevent distortion on any mating surfaces.
Now take your new clutch plate and alignment toot and offer it up to the flywheel. Make sure the plate is the correct way round. “flywheel side” is written on the side that mates with the flywheel.
Now offer up the new clutch cover. this should locate on the 3 dowel pins next to 3 of the 6 securing bolts.
screw in the 6 securing bolts by hand until starting to apply pressure on the cover plate. Then proceed to tighten them gradually in a criss cross manner. Again, this will prevent distortion of the new cover plate. the result should look like this,
While the gearbox is removed, it is always worth replacing the clutch thrust bearing. this sits in the bell housing on a carrier, Just slide the carrier of the main shaft. carefully drift the carrier off the thrust bearing. fit the new bearing to the carrier by drifting of using a vice/press. Note: never drift bearing on the outer race. this will damage the internals and undo the good work you are undertaking
The reassembly procedure is the reverse of removal
It must be said, (as pointed out bellow) This is a convenient time to check / replace the gearbox oil. Either when the tunnel has been lifted out, when the gearbox has been removed or just re fitted. Advisory: Try to ensure when checking the fluid levels that the car/ gearbox are sat as level as possible to ensure the fill plug drains the oil at the right level, weather in car or on the bench. I would recommend EP90 for topping up. EP75w-80 or EP75w-90 for filling from empty. The fill/level indicator plug is located on the right ride of the gearbox and is removed using a 1/2″ spanner on its square head. Fill slowly until you start to get some run-off coming from the fill hole. Leave the unit to stand for a few minutes thenreplace the square headed plug.
Many thanks to Chris Cook.
The GT6 Information, Restoration,and Documentation Site.